<?php
add_action( 'init', 'custom_page_rules' );

function custom_page_rules() {
	global $wp_rewrite;
	global $post;
	$first_tag = wp_get_post_tags($post->ID)[0];
	$post_name = $post->post_name;
	$author = get_the_author_meta('user_login');

	$wp_rewrite->post_structure = $wp_rewrite->root . $first_tag->slug .
		'/@' . $author . '/' . substr($post_name, strpos($post_name, "_")) ;
	//$wp_rewrite->page_structure = $wp_rewrite->root . 'page/%pagename%.html';	
}
?>